Hydrogen peroxide in liquid form has long been regarded as a disinfectant or antiseptic which is generally unstable in vitro and transient in action in vivo. In general, efforts to increase its usefulness as an antiseptic have been directed towards increasing its stability in solution and controlling its rate of decomposition. E. A. Brown, Ohio State Med. J., 42:600 (1946). While pure hydrogen peroxide of any concentration, in the absence of contaminating catalysts and in a thoroughly clean container of non-catalytic material, is relatively stable, the use of such a liquid would normally eaxpose it to any of a variety of substances which trigger its decomposition. The addition of stabilizers such as sodium stannate or 8-hydroxyquinoline, each in the presence of a soluble pyrophosphate or a phosphate-pyrophosphate mixture, reduces catalytic decomposition but, even with such stabilizers, liquid hydrogen peroxide has received only limited attention in terms of its effectiveness in killing the more resistant organisms such as bacterial spores. Toledo et al., Applied Microbiology, 26:592-7 (1973); Swartling et al., J. of Dairy Research, 35:423-8 (1968); Wardle et al., Applied Microbiology, 30:710-11 (1975).
While the use of hydrogen peroxide aerosols has been reported (see Nasa Technical Translation TTF-15, 127, of Fedyayev et al., Virucidal Action of Hydrogen Peroxide Aerosols in Decontamination of Air in an Influenza Nidus, Zhurnal Mikrobiologii, Eipidemologii i Immunobiologii, 9:137-142 (1972)), such aerosols have been presented as simply a method of dispersing the liquid so that such liquid might then perform its disinfecting function. Where surfaces are to be disinfected, efforts have been made to be certain that they are wetted by the hydrogen peroxide mist; where air (as in a room) is to be disinfected, the duration of treatment has generally been measured by the sedimentation time for most of the aerosol from the air in the room (approximately 45 minutes). The emphasis in any event has been on treatment with liquid hydrogen peroxide solutions and their possible effects in achieving the desired results.
The low tissue toxicity of the decomposition products (water and oxygen) of hydrogen peroxide is a main reason why hydrogen peroxide has received attention in the past for use as a disinfectant or antiseptic, but the instability of previous hydrogen peroxide formulations appears to have caused a diminution interest as to their ability to act as sterilizing agents. See W. C. Schumb et al., Hydrogen Peroxide, 614 et. seq. (Reinhold, 1955). Instead, other techniques have been relied upon where sterilization has been required, for example, ethylene oxide treatment, radiation, and steam sterilization. Unfortunately, such techniques are unsuitable where the articles to be sterilized are themselves incapable of withstanding the sterilizing conditions or agents, or where no harmful residuals must be present following such treatment.
U.S. Pat. Nos. 3,854,874 and 3,904,361 describe processes for sterilizing a web of packaging material by dip coating the web in a concentrated solution (10% to 40%) of hydrogen peroxide and then quickly evaporating the liquid film within 20 seconds as it travels through a hot chamber at temperatures of 80.degree. C. to 120.degree. C. where some hydrogen peroxide gas is generated for contact with the web.
Submersion of the web in concentrated liquid hydrogen peroxide solution appears to cause a shock effect on microorganisms, making them easier to kill in the hot chamber. Also, at 80.degree. C., heat alone starts to become sporicidal and its sporicidal activity increases with temperature. It is noted that steam sterilization is carried out at 120.degree. C. to 125.degree. C. Although hydrogen peroxide gas is generated for contact with the packaging web, it is believed that sterilization occurs because of the combined liquid and heat treatment.
Temperatures below 80.degree. C. are generally considered nonsporicidal and a "cold" sterilizing process would operate in this range. The conventional ethylene oxide gas sterilization process is considered a cold process and typically operates at about 55.degree. C.
The processes disclosed in the above two patents reduce the viable bacterial spore population by only 5 log orders. The Food and Drug Administration (FDA) is currently recommending that all medical and surgical products be sterilized to a probability of survival for spores, which are the most resistant of cells to kill, of 10.sup.-6 or better. This means that the sporicidal activity of a sterilizing process must be so reliable as to assure the probability of less than 1 organism out of 1,000,000 will survive a sterilization cycle.